Impotence is the consistent inability to achieve or sustain an erection of sufficient rigidity for sexual intercourse. It has recently been estimated that approximately 10 million American men are impotent (R. Shabsigh et al., "Evaluation of Erectile Impotence," Urology 32:83-90 (1988); W. L. Furlow, "Prevalence of Impotence in the United States," Med. Aspects Hum. Sex. 19:13-6 (1985)). Impotence is recognized to be an age-dependent disorder, with an incidence of 1.9 percent at 40 years of age and 25 percent at 65 years of age (A. C. Kinsey et al., "Age and Sexual Outlet," in Sexual Behavior in the Human Male, A. C. Kinsey et al., eds., Philadelphia, Pa,: W. B. Saunders, 218-262 (1948)). In 1985 in the United States, impotence accounted for more than several hundred thousand outpatient visits to physicians (National Center for Health Statistics, National Hospital Discharge Survey, 1985, Bethesda, Md., Department of Health and Human Services, 1989 DHHS publication no. 87-1751). Depending on the nature and cause of the problem, treatments include psychosexual therapy, hormonal therapy, administration of vasodilators such as nitroglycerin and .alpha.-adrenergic blocking agents (".alpha.-blockers"), oral administration of other pharmaceutical agents, vascular surgery, implanted penile prostheses, vacuum constriction devices and external aids such as penile splints to support the penis or penile constricting rings to alter the flow of blood through the penis.
A number of causes of impotence have been identified, including vasculogenic, neurogenic, endocrinologic and psychogenic. Impotence can also be a side effect of various classes of therapeutic drugs, or can be associated with various diseases, including diabetes, multiple sclerosis and sickle cell anemia. Impotence resulting from any one of these causes can be exacerbated by additional factors such as cigarette smoking, a poor diet, or the like.
Vasculogenic impotence occurs either as a result of arterial occlusion--the obstruction of adequate blood flow to the penile arteries necessary for erection--or as a result of cavernovenous leakage, i.e., excess venal outflow. As explained by Krane et al., "Medical Progress: Impotence," The New England Journal of Medicine 321(24):1628-1639 (1989), alteration in the flow of blood to and from the penis is believed to be the most frequent organic cause of impotence.
Current methods of diagnosing vasculogenic impotence or other vasculogenic erectile disorders involve measurement of penile hemodynamics after inducing an erection by direct injection of a vasoactive agent into the corporal cavernosum. For example, T. I-Sheng Hwang et al., "Impotence Evaluated by the Use of Prostaglandin E1," The Journal of Urology 141:1357-1359 (1989), describes a method for diagnosing impotence using intracavernous injection of prostaglandin E1, followed by subcutaneous injection of .sup.133 xenon to enable hemodynamic evaluation of penile vascularity. Reference may also be had to R. Virag et al., "Intracavernous Injection of Papaverine as a Diagnostic and Therapeutic Method in Erectile Failure," Angiology--Journal of Vascular Diseases, February 1984, pp. 79-87, who describe a method for diagnosing erectile failure involving intracavernous injection of papaverine and measurement of subsequent arterial changes using Doppler ultrasound.
Such diagnostic techniques, involving injection of vasoactive agents using a hypodermic needle, are painful and frequently unacceptable to patients. In addition, intracorporeal injections have been associated with priapism, development of fibrosis at the injection site and hematomas.
There is accordingly a need in the art for a noninvasive method of diagnosing erectile dysfunction, particularly vasculogenic erectile dysfunction. As used herein, the term "vasculogenic erectile dysfunction" is used to refer not only to vasculogenic impotence, but also to Peyronie's syndrome, a condition characterized by fibrosis of the cavernous tissue and associated painful and distorted penile erection. The term is also used to refer to erectile dysfunction resulting from local vascularized injury or vasculogenic changes.
Accordingly, the method of the invention is useful to diagnose vasculogenic erectile dysfunction, i.e., to determine whether or not a patient's impotence is due to vasculogenic causes. Unlike the diagnostic methods of the prior art, the present technique is noninvasive, fast, cost-effective, and easy to perform.